The key development in communication technology has been the transfer from wired to wireless communication. In the field of wireless communication, the signal propagates through the air in the form of electromagnetic waves, where the bridge of the signals between the wireless unit and the air is an antenna. That is to say, wireless communication units need antennas to transmit or receive electromagnetic waves, and they are therefore essential components of wireless communication units.
U.S. Pat. No. 6,812,892 issued on Nov. 2, 2004 discloses a multi-band antenna. As illustrated in FIG. 1, the multi-band antenna 1 comprises a first radiating strip, a second radiating strip 3, a ground portion 5, a connection strip 4 and a coaxial cable 6. The connection strip 4 interconnects the first radiating strip 2 and the second radiating strip 3. The first radiating strip 2, the second radiating strip 3, the ground portion 5 and the connection strip 4 are all disposed in the same plane. The first radiating strip 2 and the connection strip 4 are configured to function as a first planar inverted-F antenna (PIFA) operating in a higher frequency band. The second radiating strip 3 and the connection strip 4 are configured to function as a second PIFA operating in a lower frequency band.
FIG. 2 is a test chart recording for the multi-band antenna of FIG. 1, showing Voltage Standing Wave Ratio (VSWR) as a function of frequency. The bandwidth percentage of the multi-band antenna 1 is 5.7% between 2.39 GHz and 2.53 GHz, which is a narrow bandwidth. Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas.